1. Field of the Invention
This invention pertains to absorption heat-exchange systems and more particularly to high-temperature waste heat recovery systems and to control of weak solution and refrigerant flow in absorption heat-exchange systems.
2. Background of the Invention
In the past, waste heat stream recovery systems have been limited to the recovery of waste heat for relatively low temperature processes, e.g., space heating, parts cleaning, and operation of heat exchangers that require an operational temperature of less than 250° F. (121° C.). As such, previous absorption, heat-exchange machines have been limited typically to a low-temperature lithium bromide-water solution pair as the working solution.
In operating absorption heat-transfer machines, fixed restriction devices (orifices or capillary tubes) are used to control the flow of weak solution (essentially devoid of refrigerant) from the high pressure side, i.e., the generator, to the low-pressure absorber. Unfortunately such devices present a problem in that the flow rate may be lower than desired during low ambients (reduced high-side pressure) or higher than desired during high ambients (increased high side pressure). Thermal expansion valves, which vary the refrigerant flow rate, exacerbate the problem as the valve attempts to maintain an even low-side pressure.
Similar type problems exist with respect to refrigerant flow valves located between the high-pressure condenser and the low pressure evaporator. Although thermal expansion valves are available for vapor-compression systems, these valves perform poorly in absorption systems because of their low high-low side differential operating pressure. A thermal expansion valve designed for 5 refrigeration tons (RT) in a vapor compression system, is capable of 7.5 RT in an absorption system. Any attempt at using an oversized vapor-compression system valve results in a poorly functioning valve with poor control characteristics. Use of a smaller valve that does not match the absorption system capacity results in higher fluid velocities that lead to premature valve failure.
As such, it is an object of the present invention to operate the generator of an absorption heat exchanger at a solution pair (working fluid) temperature of greater than about 250° F. (121° C.) using recovered waste heat from another system.
More preferably, it is an object of the present invention to operate an absorption heat exchange machine from waste heat at a working-fluid temperature of greater than about 300° F. (149° C.).
Most preferably, it is an object of the present invention to operate an absorption heat exchange machine from waste heat at a working-fluid temperature of greater than 350° F. (177° C.).
It is a further object of the present invention to use an ammonia-water as the working fluid (solution pair) of an absorption heat-transfer machine heated with waste heat.
It is another object of the present invention to avoid degradation of the performance of the waste energy heat source.
It is an object of the present invention to use a high-temperature heat transfer fluid heated with waste heat to provide simultaneous space or process heating and a heat source for a high temperature (above 250° F. (121° C.)) absorption heat-transfer machine that provides space or process cooling.
It is an object of the present invention to alternate the use of a high pressure heat transfer fluid heat source heated with waste heat between a high-temperature absorption heat-transfer machine used for space or process cooling and second space or process heating.
It is an object of the present invention to provide an intermediate heat transfer loop based on waste heat recovery that also serves as a heat source for a high-temperature absorption heat-transfer machine.
It is an object of the present invention to use an intermediate heat transfer loop based on waste heat recovery for space heating in addition to use of the waste heat as a heating source for a high-temperature, absorption heat-transfer machine.
It is an object of the present invention to use an intermediate heat transfer loop for process heating in addition to use of the waste heat as a heating source for a high-temperature, absorption heat-transfer machine.
It is an object of the present invention to use an intermediate heat transfer loop for operating a lithium bromide absorption heat-transfer machine for cooling purposes in addition to use of the waste heat as a heating source for a high-temperature absorption heat-transfer machine.
It is an object of the present invention to improve weak solution flow control from the high to low pressure side of an absorption, heat-transfer machine.
It is an object of the present invention to provide a weak solution flow control that ensures adequate weak solution flow from the high to low pressure side of an absorption, heat-transfer machine without harsh on/off regulation.
It is an object of the present invention to provide a weak solution flow control that ensures adequate weak solution flow from the high to low pressure side of an absorption, heat-transfer machine over a wide range of pressures.